As a food container such as barrel or tank for transporting or storing drinks (for example, beer, juice and milk) or liquid foods or as a food container such as a large tank used in a tank truck, a container made of glass, plastic, metal or the like is employed depending on the use purpose. Among these, a metal container is widely used because of its excellent durability. In particular, a stainless steel container is used for general purposes because it is resistant to rusting. In the meantime, a glass container serves as a convenient container in view of advantages such as freedom in shaping and low cost.
Containers for transportation or storage are repeatedly used in many cases and are used outdoors on many occasions. Therefore, containers where the outside or filling port is difficult to soil and even when soiled, can be easily washed are required. Glass containers have a thick-wall structure to compensate for its weak mechanical strength, as compared with the case of a stainless steel container, and therefore are heavier as much. Accordingly, there is a need for reducing the weight of glass containers.
To ensure the food container is difficult to soil, a surface treatment method such as a method of treating the container surface with fluorine, for example, by coating a fluororesin thereon to enlarge the contact angle with water, namely, improve the water repellency, is known.
However, in treating the surface of a food container, for example, by coating a fluororesin thereon, the color of the coating agent used adversely affects the color of the food container. Therefore, this is disadvantageous as a surface treatment method of food containers where the feel of cleanliness is needed. Furthermore, the coating may be abraded or peeled off during use and there is a problem in the use of container over a long period of time.
In addition, the mechanical strength of a food container made of glass disadvantageously decreases when the thickness of a wall of the container is reduced in order to reduce the weight of the container.